import java.util.Scanner;
public class Problem2 {

	public static void main(String[] args) {
		Scanner scanner = new Scanner(System.in);
		double a =scanner.nextDouble();
	try {	
		double b =scanner.nextDouble();
		double c = 4*a*b;
		System.out.printf("%.2f",c);
	    }finally{
			scanner.close();
	    }
	}

}